1. Field of the Invention
The present invention relates to a module employed in systems using wavelength division multiplex.
2. Description of Related Art
Wavelength division multiplex (WDM) has been extensively developed as an optical transmission technique which is expected to be applied to the backbone line for next generation Internet. This WDM technique makes it possible to bi-directionally transmit a large amount of data by making use of light waves with different wavelengths to be transmitted through a single optical fiber in order to multiplex a plurality of channels.
In the case of the optical network based on the WDM technique, an optical add drop multiplexer (OADM) optical module is used to extract or interpose a light wave having a particular wavelength from a plurality of light waves which have different wavelengths and propagate through a single optical fiber. An OADM optical module is proposed as a technique for extracting or interposing a light wave having a particular wavelength from a plurality of light waves which have different wavelengths by combining optical wave guide paths and a wavelength selective filter (refer to Japanese Patent Published Application No. Hei 11-109149).
The optical wave guide paths for use in the technique as described above are fabricated by laminating an inorganic material such as quartz, a plastic and the like on a substrate by the silicon wafer technique or CVD (Chemical Vapor Deposition). However, these techniques require an expensive manufacturing facility and many manufacturing steps. Particularly, the manufacture cost tends to increase by the requirement of high-precision processing for reducing the gap between the filter and the light path. Furthermore, since the optical wave guide paths are formed on the substrate, there is a problem that the geometry is generally restricted by the profile of the substrate.